补全 P0：筛选、访客图片与双向输入状态

- 工作台会话列表支持状态/紧急筛选
- 访客 Widget 支持 jpg/png/gif 图片预览发送
- WebSocket 支持访客输入中通知客服，客服输入中通知访客
- 工作台聊天区展示「访客正在输入」动画

server/internal/ws/ws_test.go

@@ -67,3 +67,34 @@ func TestBroadcastToVisitorRestrictsSession(t *testing.T) {
 		}
 	}
 }
+
+func TestBroadcastToSessionStaffExcludesVisitor(t *testing.T) {
+	hub := NewHub()
+	go hub.Run()
+
+	sessionID := uint(31)
+	agentID := uint(3)
+	assigned := &Client{TenantID: 1, UserID: agentID, Role: "agent", Kind: "agent", Send: make(chan []byte, 1)}
+	otherAgent := &Client{TenantID: 1, UserID: 4, Role: "agent", Kind: "agent", Send: make(chan []byte, 1)}
+	supervisor := &Client{TenantID: 1, UserID: 5, Role: "supervisor", Kind: "agent", Send: make(chan []byte, 1)}
+	visitor := &Client{TenantID: 1, Kind: "visitor", SessionID: &sessionID, Send: make(chan []byte, 1)}
+	for _, client := range []*Client{assigned, otherAgent, supervisor, visitor} {
+		hub.register <- client
+	}
+
+	hub.BroadcastToSessionStaff(1, &agentID, []byte(`{"type":"typing","data":{"from":"visitor"}}`))
+	for _, client := range []*Client{assigned, supervisor} {
+		select {
+		case <-client.Send:
+		case <-time.After(time.Second):
+			t.Fatalf("工作人员未收到输入状态：%+v", client)
+		}
+	}
+	for _, client := range []*Client{otherAgent, visitor} {
+		select {
+		case <-client.Send:
+			t.Fatalf("不应收到的客户端收到消息：%+v", client)
+		default:
+		}
+	}
+}